1. Field of the Invention
The present invention generally relates to a probe card, and more particularly to a CIS circuit test probe card.
2. Description of the Prior Art
Testing of a CMOS Image Sensor (CIS) can be implemented using a CIS test probe card. While functional in some ways, the conventional CIS test probe card has deficiencies in others, especially when the size of CIS chip is reduced and/or the required testing environment is strict.
Diagrammatic structures of both a conventional CIS chip and a conventional application of a CIS test probe card are separately shown in FIG. 1A and FIG. 1B. As shown in FIG. 1A, each CIS chip 10 has a light sensing region 11 and at least one pad 12 located around the light sensing region 11. As shown in FIG. 1B, light 165 is emitted from a light source 16 (such as a lamp) and then passed through a tester 17 with a hole 175 before the light 165 is projected through a conventional CIS test probe card 18 and onto a wafer 19 having CIS chips 195. Here, the conventional CIS test probe card 18 has probes 185 capable of contacting the CIS chips 195, such that the signals are transmitted from the CIS chips 195 through the CIS test probe card 18 and to the tester 17 capable of analyzing the signals. Moreover, if necessary, a collimator can be located close to the light source 16 such that the light 165 is collimated.
A first deficiency in this context is the non-uniformity (divergency) of the light 165 projected onto the CIS chips 195. To provide better testing condition, it is better that all CIS chips 195 receive the same projected light 165, such that different signals (from different CIS chips 195) are induced by the differences among the CIS chips 195. However, as the emitted light 165 is not perfectly parallel light, its projection onto different portions of the wafer (onto different CIS chips 195) will have different incidental angles, which in turn will induce different signals on the different CIS chips 195, even those CIS chips 195 that are essentially similar. Of course, a simple solution is using a better light source 16, such as a highly qualify laser. However, the cost also will be significantly increased, and the laser may not be perfectly collimated either.
A second deficiency is the shadow effect induced by the probes 185. For conventional commercial products, the CIS test probe card 18 has a large hole 188 which covers all CIS chips 195 on the wafer 19, with the probes 185 being located near the large hole 188. Therefore, the probes 185 connected to the CIS chips 195 on the center portion of the wafer 19 usually will interact with the light 165 projected to the CIS chips 195 on the center portion of the wafer 19. As a result, shadows of the probes 185 are almost unavoidable. In addition, even if the shadows are reduced or avoided, the effect of light scattered by the probes 185 also can be unavoidable.
It is necessary to develop easy and low cost approaches to overcome the above deficiencies.